Fokker 50 - Electrical System
GENERAL
Fleet differences
Within the fleet three different supplementary electrical power suppliers can be found, the
following table is showing the differences:
Type I
AC external power
DC external power
APU
Type II
AC external power
NO DC external power
APU
Type III
AC external power
NO DC external power
NO APU
Description
The aircraft electrical system comprises 115 V/400 Hz three phases AC power and 28 V DC
power and can be controlled from the ELECTRIC panel and the APU panel. Failures will be
detected and the relevant alerts presented.
AC power
AC power can be supplied by two engine driven generators, an APU driven generator, or an
AC external power source. During normal operation GEN 1 and GEN 2 supply AC bus 1 and
AC bus 2 respectively. The AC EMER bus 1 is also energized. If a generator becomes
inoperative, AC power transfer is automatic. The output from one engine driven generator is
sufficient to meet the aircraft electrical power requirements. AC power from the APU
generator is available on the ground only.
DC power
DC power is supplied by two Transformer Rectifier Units (TRU), two batteries or an external
DC power source. TRU 1 and TRU 2 supply DC bus 1 and DC bus 2 respectively. The DC
EMER buses are also energized. The output from one TRU is sufficient to meet all aircraft
DC power requirements. DC power supply includes two battery chargers. They are powered
from AC bus 1 and AC bus 2 respectively.
The batteries supply power to:
• DC EMER bus 1 and DC EMER bus 2.
• AC EMER bus 1 via a static inverter.
• AC ground service bus via a ground service inverter.
The batteries can supply power for at least 30 minutes.
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Fokker 50 - Electrical System
Functional diagrams
Functional diagrams - Type I
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Fokker 50 - Electrical System
Functional diagrams - Type II
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Fokker 50 - Electrical System
Functional diagrams - Type III
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Fokker 50 - Electrical System
AC POWER
Generation
Normal AC generation
There are four sources of AC power; two engine driven generators, an APU generator, and
AC external power.
Engine driven generators
The engine driven generator is mounted in the same assembly as the Constant Speed Drive
(CSD). This assembly is called an Integrated Drive Generator (IDG). The function of the CSD
is to ensure that the generator rotational speed is constant, thus resulting in a constant
frequency of 400 Hz.
When for any reason the temperature of the oil inside the CSD starts to rise to a point where
seizure might occur, a thermal disconnect separates the CSD from the engine. Rotation
ceases and the IDG is protected against serious damage. In this case it is not possible to reengage the CSD.
The IDG output is controlled by a Generator Control Unit (GCU). When voltage and
frequency are within predetermined limits the GCU automatically connects the generator to
the aircraft electrical system. The GCU will automatically disconnect the generator from the
aircraft electrical system if a failure is detected.
APU driven generator (Type I and II)
The APU driven generator provides auxiliary AC power and can be used on the ground only.
The generator output is controlled by a GCU. When the voltage and frequency of the
generator are within limits, the AVAIL light, at the APU GENERATOR pushbutton illuminates.
When this pushbutton is depressed from AVAIL to ON, the entire electrical system is
energized. The generator is not equipped with a CSD since the APU runs at a constant
speed.
When AC power is supplied by one engine generator and the APU generator is available, the
engine generator will supply its respective AC bus while the APU generator will supply the
other AC bus. When AC power is supplied by both engine generators and the APU generator
is available the engine driven generators have priority.
AC external power (All)
A receptacle on the right-hand side of the front fuselage is used to connect AC external
power to the aircraft. A Ground Power Control Unit (GPCU) is provided to protect the aircraft
electrical system against damage. When AC external power is plugged in and meets
minimum quality standards, the AVAIL light, at the EXTERNAL POWER pushbutton
illuminates and the AC ground service bus is energized automatically. When this pushbutton
is depressed from AVAIL to ON, the entire electrical system is energized and the EXT PWR
FED light at the connector is ON.
.
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Fokker 50 - Electrical System
When AC power is supplied by one engine generator and the AC external power is available,
the engine generator will supply its respective AC bus while the AC external power will
supply the other AC bus. When AC power is supplied by both engine generators and AC
external power is available the engine driven generators have priority.
For type I and II
When the APU generator and AC external power are available, the APU generator power
has priority.
Distribution
The AC electrical system incorporates:
• AC bus 1 and AC bus 2.
• AC EMER bus 1
• AC ground service bus.
AC bus 1 and AC bus 2
AC bus 1 and AC bus 2 are normally supplied by the respective generator. If either of the
generators becomes inoperative, both AC bus 1 and AC bus 2 are automatically supplied by
the operative generator. An AUTO AC X-FEED push button is provided to cancel this
automatic crossfeed if required.
NOTE:
AC galley power is automatically shed during all single-generator operation.
AC EMER bus 1
AC EMER bus 1 is normally connected to AC bus 1. If both AC buses become de-energized,
the batteries are connected automatically to a static inverter and the output of the inverter is
fed to AC EMER bus 1, to provide essential AC power.
AC ground service bus
The AC ground service bus is energized both on the ground and in flight when AC power is
available. Without AC power available on the ground, the AC ground service bus can be
energized by the batteries via a ground service inverter.
A ground service TRU provides power to the DC ground handling bus.
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Fokker 50 - Electrical System
Functional diagram
Functional diagram - Type I and Type II
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Fokker 50 - Electrical System
Functional diagram - Type III
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Fokker 50 - Electrical System
Controls and indicators
Controls and indicators – Type I
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Fokker 50 - Electrical System
Controls and indicators – Type II
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Fokker 50 - Electrical System
Controls and indicators – Type III
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Fokker 50 - Electrical System
Controls and indicators – Type I en Type II
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Fokker 50 - Electrical System
Alerts
CONDITION(S) / LEVEL
AURAL
MWL/MCL
CAP
LOCAL
BAT PWR
ONLY
LOSS OFF BOTH
GENERATORS
3
AC SUPPLY
WARNING
BUS
FAULT
AUTO AC X-FEED
FAULT
GENERATOR + AUTO
X-FEED FAULT
2
GENERATOR
CAUTION
FFAULT
BUS
FAULT
GENERATOR
FAULT
GENERATOR FAULT
2
CAUTION
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Fokker 50 - Electrical System
CONDITION(S) / LEVEL
AURAL
MWL/MCL
CAP
LOCAL
AUTO AC X-FEED
FAULT
AUTO AC X-FEED
FAULT
2
CAUTION
BUS FAULT
BUS
FAULT
2
CAUTION
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Fokker 50 - Electrical System
DC POWER
Generation
Normal DC generation
Normal DC power is supplied by two TRU’s, which are connected to the AC buses.
Transformer rectifier unit
Each TRU receives AC power and provides DC power to the respective DC bus and DC
EMER bus. The TRU is automatically disconnected in case of overheat or reverse current.
Battery power
Battery power is provided by two batteries connected in parallel. Each battery has a battery
charger that receives power from the respective AC bus. Each battery charger monitors the
condition of the respective battery and regulates the charging current to avoid battery
overheat. In case of a battery overheat the L/R BAT OVHT light on the CAP illuminates. A
BATTERIES switch is provided to connect the batteries to the DC system and should be ON
during all normal operating conditions. If the batteries are the only available source of power,
the BAT PWR ONLY light illuminates. During battery power only operation, selected DC
electrical loads are automatically shed to provide a minimum of 30 minutes battery power
supply.
DC External power (Type I)
A receptacle on the RH side of the front fuselage is used to connect DC external power to
the aircraft. When DC external power is plugged in and if it meets minimum quality standards
the AVAIL light illuminates. When DC power external power is connected to aircraft systems
several services are not available. See system operation as well. AC power has priority over
DC external power.
Distribution
The DC electrical system incorporates:
• DC bus 1 and DC bus 2.
• DC EMER bus 1 and DC EMER bus 2.
• DC ground handling bus.
DC bus 1 and DC bus 2
DC bus 1 and DC bus 2 are normally supplied by TRU 1 and TRU 2 respectively. If either of
the DC buses becomes de-energized, both DC buses could be powered by one TRU if the
DC X-FEED is manually switched ON. Both buses are interconnected automatically during
engine start.
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Fokker 50 - Electrical System
DC EMER bus 1 and DC EMER bus 2
DC EMER bus 1 and DC EMER bus 2 are normally supplied by TRU 1 and TRU 2
respectively. If either of the TRU’s becomes de-energized, both EMER DC busses will be
powered automatically by the operative TRU. If both TRU’s become de-energized, both
EMER DC busses are automatically connected to the batteries, to provide essential DC
power for at least 30 minutes.
DC ground handling bus
Power is automatically available to the DC ground handling bus from the batteries or the AC
external power source.
The DC ground handling bus supplies the following services:
• Passenger door operation
• Hydraulic fluid quantity checks
• Refueling
There are no lights or pushbuttons in the flight deck directly related to the ground handling
buses.
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Fokker 50 - Electrical System
Functional diagram
Functional diagram - Type I
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Fokker 50 - Electrical System
Functional diagram - Type II and Type III
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Fokker 50 - Electrical System
Controls and indicators
Controls and indicators - Type I
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Fokker 50 - Electrical System
Controls and indicators - Type II and Type III
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Fokker 50 - Electrical System
Alerts
CONDITION(S) / LEVEL
AURAL
MWL/MCL
CAP
LOCAL
CHARGER
L BAT
OVHT
FAULT
BATTERY OVERHEAT
3
OR
WARNING
R BAT
OVHT
BUS FAULT
BUS
FAULT
2
CAUTION
CHARGER
BATTERY CHARGER
FAULT
2
FAULT
CAUTION
TRU
TRU FAULT
2
CAUTION
FAULT
BUS
FAULT
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Fokker 50 - Electrical System
CIRCUIT BREAKERS
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Fokker 50 - Electrical System
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Fokker 50 - Electrical System
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Fokker 50 - Electrical System
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Fokker 50 - Electrical System
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Fokker 50 - Electrical System
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Fokker 50 - Electrical System
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Fokker 50 - Electrical System
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Fokker 50 - Electrical System
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Fokker 50 - Electrical System
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Fokker 50 - Electrical System
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Fokker 50 - Electrical System
SYSTEM OPERATION
System data
DISPLAY SELECTOR
BUS VOLT
DC/EMER DC
AC
EMER AC
EXT PWR
VOLT-FREQ
GEN
LOAD
(%)
CONTINUOUS
5 MIN
5 SEC
VOLT
FREQ
BAT
LOAD (A)
VOLT
TRU
LOAD
(%)
CONTINUOUS
2 MIN
5 SEC
VOLT
LH ELECTRIC DISPLAY
BUS 1
26 - 31
111 - 119
111 - 119
VOLT
110 - 120
GEN 1
RH ELECTRIC DISPLAY
BUS 2
26 - 31
111 - 119
FREQ
385 - 415
GEN 2
100
113
150
111 - 119
395 - 405
BAT 1
+40 / -40
23 - 32
TRU 1
100
113
150
111-119
395 – 405
BAT 2
+40 / -40
23 - 32
TRU 2
100
133
300
26 - 31
100
133
300
26 - 31
Type I
When on DC external power amongst other systems the following services are not available:
• AHRS Cooling.
• Avionics rack cooling.
• Instrument cooling.
• Recirculation fans.
• Window heating.
• Hydraulic system electrical pump.
• Water quantity indication.
Due to lack of avionics cooling the use of DC external power must be restricted to a few
minutes when the outside air temperature is 25 degrees or above.
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